The present invention relates to a heat alarm device.
Heat alarm devices for sensing heat, for example from a fire, are well known in the art.
Typically such heat alarms comprise a body containing control and drive circuitry, a heat sensor extending from the body and a cage located around the heat sensor in a manner that allows free flow of air past the sensor. The cage is rigid and is typically made of such a size that it stands well clear of the sensor such that its thermal mass has minimum impact on the response of the sensor to a rise in ambient temperature.
The cage is necessary to present the heat sensor at a position removed from the large thermal mass of the electronics and body of the alarm, whilst also protecting the heat sensor from damage, and preventing the sensor (which will be attached to a source of electricity) being accidentally touched by anyone.
The sensor is generally centrally located so that the effect of the thermal mass of the body is substantially equal irrespective of the direction from which the heat originates (e.g. there is no heat shadow created by off-setting the sensor) and the protective cages are generally quite large relative to the sensor so that air can freely circulate around the sensor.
According to a first aspect of the invention there is provided a heat alarm apparatus comprising: a housing defining a body, a sensor mounting panel located on said body, a heat sensor extending from said sensor mounting panel; and a control circuit configured to detect a temperature rise at the heat sensor and output an alarm signal in response thereto. At least the surface of the sensor mounting panel from which the heat sensor extends is a dark colour.
In a preferred arrangement the colour of the surface of the sensor mounting panel is either neutral, or has a hue ranging from purple to green, and has a value of 3 or less on the Munsell Colour System. More preferably the colour of said surface of the sensor mounting panel may have a value of 2 or less, or of 1 or less, on the Munsell Colour System.
By maintaining a dark colour for the surface the response time of the sensor to a change in heat of the environment in which it is placed, either radiated heat from a nearby heat source or of the air temperature, is increased so that the alarm can indicate a danger in a quicker response time.
The surface of the sensor mounting panel from which the heat sensor extends may optionally be provided with a plurality of embossed or impressed features thereon. The plurality of embossed or impressed features may comprise a plurality of pyramid shaped features extending from the surface or a plurality of pyramid shaped impressions extending into the surface, however other shapes may be used. As, in the case of a fire, the heat is likely to come from a specific direction, then having a plurality of angular shaped protrusions or recesses will increase the area of the mounting panel for which the angle of sight to the heat source, and therefore the angle of incidence of the radiated heat, is increased which will improve the heat absorption/radiation from the mounting panel. It is also believed that the surface features may increase heat transfer when air passes thereover. The effect is measureable and demonstrable and although the mechanics of the benefit described herein are believed to be accurate they have not been irrefutably proven and the effect may be for reasons other than those stated.
In one arrangement the sensor mounting panel may be concave. Again this is believed to assist with the reflected, radiated and absorbed heat, which together increase the speed at which the heat sensor registers a change in temperature. Additionally, having a concave sensor means that a greater portion of the reflected and radiated heat will be reflected/radiated in the direction of the heat sensor which is located substantially in the centre of the sensor mounting panel.
The sensor mounting panel comprises a moulding of a coloured plastic, or alternatively the sensor mounting panel may have a coloured coating (e.g. a paint) thereon.
A protective cage preferably extends from the housing and forms an enclosure between the protective cage and the sensor mounting panel, and the heat sensor is located in said enclosure. As the heat sensor extends from the mounting panel, and needs free air from the environment in which it is placed to circulate around it, the purpose of the cage is twofold. Firstly it protects the heat sensor from damage, and secondly it contributes to the electrical safety of the alarm by assisting in preventing fingers or the like from coming into contact with the sensor.
The sensor mounting panel may be recessed in the housing, this assists in contributing to the protection of the sensor therein.
According to a second aspect of the invention there is provided a heat sensing module for a heat alarm apparatus. The heat sensing module comprises: a sensor mounting panel; a heat sensor extending from said sensor mounting panel; and a control circuit configured to detect a temperature rise at the heat sensor and output an alarm signal in response thereto. At least the surface of the sensor mounting panel from which the heat sensor extends is a dark colour.
The colour of said surface of the sensor mounting panel is preferably the same as those described above in relation to the first aspect of the invention.
The surface of the sensor mounting panel from which the heat sensor extends may be provided with a plurality of embossed or impressed features thereon. The plurality of embossed or impressed features may comprise a plurality of pyramid shaped features extending from the surface or a plurality of pyramid shaped impressions extending into the surface.
The sensor mounting panel can be concave. The sensor mounting panel comprises a moulding of a coloured plastic, or alternatively the sensor mounting panel may have a coloured coating thereon.
Preferably a protective cage extends from said housing and forms an enclosure between said protective cage and said sensor mounting panel, and the heat sensor is located in said enclosure.